Wear compensating die



A. L. REESE July 9, 1968 Filed May 1, 1961 IN VEN TOR.

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.T LI z ARTHUR L. REESE H/S ATTORNEYS United States Patent 3,391,657WEAR CUMPENSATING BEE Arthur L. Reese, San Francisco, Calif assignor toCalifornia Pellet Mill Company, San Francisco, Calif., a corporation ofCalifornia Filed May 1, 1961, Ser. No. 106,914 7 Claims. (Cl. 107-44) Myinvention relates to extrusion of material and formation of pellets andmore particularly to a die for such purpose.

Dies of the type to which the present invention relates are for useprimarily in pellet mills of the type illustrated and described in thepatent to Edgar T. Meakin No. 2,240,660, dated May 6, 1941, forExtrusion Mill, though not necessarily restricted thereto, whereotherwise applicable. Such a die may be in the form of a ring having acompression side and a discharge side, the compression side beingnormally traversed, in the operation of such mill, by extrusion meansusually in the form of rolls, while the discharge side is the side fromwhich emerge the extrusions which are severed into pellets as theextrusions emerge from the die.

In such a die, the diameter of the die holes is dictated by the diameterof the pellets desired, while the length of the die holes is determinedby the desired firmness of the extruded product. If the holes be tooshort, the product will be too soft, while if the holes are too long,the product will be either too hard or the die holes may plug and failto function. A countersink at the entrance to each die hole is oftenprovided to facilitate the guidance of loose maten'ai into the die holesfor extrusion, the number of die holes in a die being the maximumpermissible and are usually sufficient closely spaced as to leave aminimum land surface between countersinks.

It the length of the die holes essential to produce a pellet of theproper consistency, is such as would otherwise result in a die ofinsutlicient thickness to withstand the strains and stresses encounteredin use, then the die must be made to a thickness sufficient to withstandsuch stresses and strains. To retain, under these conditions, theeffective extrusion passage necessary to realize proper firmness of theextruded product, the die hole passages are counter-bored from thedischarge side of the die sufficient to leave a working section of theproper length.

Material under extrusion in the working section, exits therefrom atelevated temperature and has a tendency to swell. The diameter of thecounter-bore must be such as to permit of such swelling andsubstantially free discharge of the extrusion therethrough to thedischarge side of the die.

Pellet mill dies of the type referred to, suffer from the abrasivenessof materials extruded therethrough, resulting in Wearing down of thedies on the compression side thereof, thus shortening the extrusionlength of the work section of the die hole.

Along with this, the abrasive character of the material produces awearing of the walls of the working section of the die holes to cause anenlargement thereof.

Inasmuch as the forming of an extrusion to a desired firmness is afunction of resistance to movement of material through the die hole, itfollows that any reduction in such resistance will bring about acorresponding reduction in firmness of the extrusion of a particularmaterial. The wearing of the die surface and the die hole walls, bothfunction toward reducing such resistance, and consequently, a point isreached in the use of a die, when the extrusion and the resultingpellets no longer are of the desired firmness and the die is no longerusable for this purpose.

Among the objects of the present invention are:

(1) To provide a novel and improved pellet mill die;

3,331,557 Patented July 9, 1968 (2) To provide a novel and improvedpellet mill die which will have an extended life expectancy;

(3) To provide a novel and improved pellet mill die which will maintainsubstantially constant resistance to the extrusion of a material, over alonger period of use;

(4) To provide a novel and improved pellet mill die which will maintainan acceptable firmness of the pelleted product in spite of wear on thedie;

(5) To provide a novel and improved pellet mill die which willinherently compensate for die wear to maintain an acceptable firmness ofthe pelleted product.

Additional objects of my invention will be brought out in the followingdescription of a preferred embodiment of the same, taken in conjunctionwith the accompanying drawings, wherein:

FIGURE 1 is a fragmentary view, partly in section, of a die embodyingthe features of the present invention; and

FIGURE 2 is an enlarged view illustrative of a sectional portion of thepellet mill die of FIGURE 1 and depicting the details of a die holetherethrough incorporating the features of the present invention.

Referring to the drawing for details of my invention in its preferredform, the die has a compression side 1 and a discharge side 3 connectedby a plurality of die holes 5 therethrough from its compression side toits discharge side. Each such die hole is made up of three sections: aworking section 7 proximate the compression side of the die, thecompression side of the die may inelude a countersink 9; a reliefsection 11 at the discharge side of the die; and an intermediate flaringsection 13 connecting the working section to the relief section andwhich, in accordance with the present invention, must bear certain welldefined relationships to the working section 7 of the die hole.

The diameter of the working section 7, in accordance with conventionalpractice, will be such. as to produce a product of desired diameter,while the length of the working section will be such as to produce thedesired firmness in such product. Wear on the compression side of thedie will have the effect of shortening the length of the working sectionand thereby reduce the firmness of the extruded product. An increase inthe diameter of the working section, due to wear of the walls thereof,will not only tend to further reduce the firmness of the product, butwill also serve to slightly increase the diameter thereof. While suchslight increase in diameter of the extruded product may be tolerated,the combined tendency to reduce the firmness of the product willultimately result in a soft product which would not be acceptable With aflaring intermediate section of the die hole present, it will beappreciated that as the diameter of the working section is increased,say from d to D, the length of the working section will effectively beincreased by an increment L, or in other words, will be caused to growinto the flared intermediate section, which growth will introduceresistance to movement of material through the working section, and thuswill be in the proper direction to compensate for effects of wear on thedie.

However, to realize effective benefits from this, the included angle Aof the intermediate section, should be such as to create a growth in theworking section of the die hole sufficient to match the rate at whichthe working section shortens due to wear on the compression side of thedie, and preferably should exceed such rate of shortening, by an amountsufficient to also compensate for the increase in diameter of theworking section of the die hole.

Illustrative of the magnitude of values and dimensions involved, onemight cite as an example, a die developed for use on dried sugar beatpulp, wherein the G working section of each die hole is of an initialdiameter of inch and an initial length of /2 inch, the thickness of thedie is 2% inches, while the included or flare angle of the intermediatesection of the die hole is of the order of 334 and 48.

With a die incorporating the features of the present invention, the lifeexpectancy of the die will no longer be determined by the loss infirmness of the product of the machine, but will be determined, for themost part, by cross sectional enlargement of the working section of thedie hole to a point where the wall surfaces become rough and pitted orthe die becomes unduly weakened by the resulting thinning of the wallstructure between holes.

Inasmuch as the die will, during the increased portion of its lifeexpectancy, be functioning with the working sections of the die holes atincreased diameters, the relief sections of the die holes willpreferably be of slightly larger diameter than otherwise, in order toadequately accommodate and provide for extrusions under theseconditions.

While one might conceivably run the flared sections to the dischargeside of the die and thereby eliminate the relief section entirely, itwill be appreciated that such flared sections would terminate at thedischarge side of the die in openings of excessive diameter, and that tomaintain conventional spacing between die holes in a conventional dieunder these conditions, would necessarily cause considerable overlappingof the flared sections as they approached the discharge side of the die,thereby structurally weakening the die. If such overlapping is to beavoided, it would necessarily mean a wide separation of the die holesand accordingly a corresponding reduction in the capacity of the die.For this reason, I prefer to terminate the flared sections in reliefsections provided in the discharge side of the die.

From the foregoing description of my invention in its preferred form, itwill be apparent that the same fulfills all the objectives of myinvention. The minimum spacing between die holes and consequently themaximum capacity of the die may be maintained, while materiallyincreasing the life expectancy of the die.

Accordingly, while I have illustrated and described my invention in itspreferred form, the same is subject to alteration and modificationwithout departing from the underlying principles involved, and Iaccordingly do not desire to be limited in my protection to the specificdetails illustrated and described, except as may be necessitated by theappended claims.

I claim:

1. An extrusion die having a compression side and a discharge side, adie hole therethrough defined by a hole wall extending from itscompression side to its discharge side, said die hole including aworking section proximate the compression side of said die and of adiameter to produce an extrusion of a desired cross section, and meansto prevent the shortening of said working section to maintain adesirable consistency of material extruded through said die and therebyextend the normal useful life of said die, said means comprising aflaring section, said flaring section having a wall surface defining anangle of flare from said working section such as to cause said workingsection to grow at a rate commensurate with the rate of wear of said dieon its compression side, to maintain a desirable consistency of materialextruded through said die and thereby extend the normal useful life ofsaid die.

2. An extrusion die having a compression side and a discharge side, adie hole therethrough defined by a hole wall extending from itscompression side to its discharge side, said die hole including aworking section proximate the compression side of said die and of adiameter to produce an extrusion of a desired cross section, a reliefsection adjacent the discharge side and of larger cross sectional areathan said Working section, and means to prevent the shortening of saidWorking section to maintain a desirable consistency of material extrudedthrough said die and thereby extend the normal useful life of said die,said means comprising an intermediate flaring section connecting theworking section with said relief section, said flaring section having a'wall surface defining an angle of flare from said working section suchas to cause said working section to grow at a rate at least equal to therate of wear of said die on its compression side, to maintain adesirable consistency of material extruded through said die and therebyextend the normal useful life of said die.

3. An extrusion die having a compression side and a discharge side, adie hole therethrough defined by a hole wall extending from itscompression side to its discharge side, said die hole including aworking section proximate the compression side of said die and of adiameter to produce an extrusion of a desired cross section, a reliefsection adjacent the discharge side of said die and of larger crosssectional area than said working section, and means to prevent theshortening of said working section to maintain a desirable consistencyof material extruded through said die and thereby extend the normaluseful life of said die, said means comprising an intermediate flaringsection connecting the working section with said relief section, saidflaring section having a wall surface defining an angle of flare fromsaid working section such as to cause said working section to grow at arate sufficient to compensate for enlargement of said hole and wear ofsaid die on its compression side, to maintain a desirable consistency ofmaterial extruded through said die and thereby extend the normal usefullife of said die.

4. An extrusion die having a compression side and a discharge side, adie hole therethrough defined by a hole wall extending from itscompression side to its discharge side, said die hole including acountersink in the compression side and a working section adjacent saidcountersink of a length adequate to produce an extrusion of desiredfirmness, means to prevent the shortening of said working section tomaintain a desirable consistency of material extruded through said dieand thereby extend the normal useful life of said die, said meanscomprising an outwardly flaring section intermediate said workingsection and discharge side of said die and having a wall surfacedefining an angle of flare such that enlargement of the cross section ofsaid working section and wear of the die on the compression side in use,will be effectively compensated by an inherent growth of said workingsection at the expense of said tapered section, to maintain a desirableconsistency of material extruded through said die and thereby extend thenormal useful life of said die.

5. An extrusion die having a compression side and a discharge side and athickness sufficient to withstand working stresses during extrusion ofmaterial through said die, a die hole therethrough defined by a holewall from its compression side to its discharge side, said die holeincluding a working section of a desired diameter proximate thecompression side of said die and of a length to produce an extrusion ofa desired firmness at said diameter, a counter-bore relief sectionadjacent the discharge side of said die and of a diameter to permitsubstantially full expansion of material entering said relief sectionfor the life of said die, and means to prevent the shortening of saidworking section to maintain a desirable consistency of material extrudedthrough said die and thereby extend the normal useful life of said die,said means comprising an intermediate flaring section connecting saidworking section to said relief section and having a wall surfacedefining an angle of flare such that the rate of growth of said workingsection in the longitudinal direction resulting from normal increase indiameter through use, will compensate for normal wear on the compressionside of said die.

6. An extrusion die having a compression side and a discharge'side and athickness suflicient to withstand working stresses during extrusion ofmaterial through said die, a die hole therethrough defined by a holewall from its compression side to its discharge side, said die holeincluding a countersink in the compression side and a working section ofa desired diameter adjacent said countersink and of a length to producean extrusion of a desired firmness at said diameter, a counter-borerelief section adjacent the discharge side of said die and of a diameterto permit substantially full expansion of material entering said reliefsection for the life of said die, and means to prevent the shortening ofsaid working section to maintain a desirable consistency of materialextruded through said die and thereby extend the normal useful life ofsaid die, said means comprising an intermediate flaring sectionconnecting said working section to said relief section and having a wallsurface defining an angle of flare such that the rate of growth of saidworking section in the longitudinal direction resulting from normalincrease in diameter through use, will compensate for both said increasein diameter and normal wear on the compression side of said die.

7. An extrusion die having a compression side and a discharge side, adie hole therethrough defined by a hole wall extending from itscompression side to its discharge side, said die hole including aworking section proximate the compression side of said die and of adiameter to produce an extrusion of a desired cross section, a reliefsection adjacent the discharge side of said die and of largercross-sectional area than said working section, and means to maintain adesirable consistency of material extruded through said die and therebyextend the normal useful life of said die, said means comprising anintermediate flaring section connecting the working section with saidrelief section, said flaring section having a wall surface defining anangle of flare from said working section such as to cause said workingsection to grow at a rate sufficient to compensate for enlargement ofsaid hole to maintain deasirable consistency of material extrudedthrough said die and thereby extend the normal useful life of said die.

References Cited UNITED STATES PATENTS 2,059,486 11/1936 Payne et a1.107-8.35 2,902,715 9/1959 Norman 18l2 2,984,173 5/1961 Roche et a1100-93 FOREIGN PATENTS 205,253 1/ 1957 Australia.

WALTER A. SCHEEL, Primary Examiner. JOSEPH D. SEERS, CHARLES A.WILLMUTH,

Examiners.

CARL J. FRIBERG, JOSEPH SHEA,

Assistant Examiners.

1. AN EXTRUSION DIE HAVING A COMPRESSION SIDE AND A DISCHARGE SIDE, ADIE HOLE THERETHROUGH DEFINED BY A HOLE WALL EXTENDING FROM ITSCOMPRESSION SIDE TO ITS DISCHARGE SIDE, SAID DIE HOLE INCLUDING AWORKING SECTION PROXIMATE THE COMPRESSION SIDE OF SAID DIE AND OF ADIAMETER TO PRODUCE AN EXTRUSION OF A DESIRED CROSS SECTION, AND MEANSTO PREVENT THE SHORTENING OF SAID WORKING SECTION TO MAINTAIN ADESIRABLE CONSISTENCY OF MATRIAL EXTRUDED THROUGH SAID DIE AND THEREBYEXTEND THE NORMAL USEFUL LIFE OF SAID DIE, SAID MEANS COMPRISING AFLARING SECTION, SAID FLARING SECTION HAVING A WALL SURFACE DEFINING ANANGLE OF FLARE FROM SAID WORKING SECTION SUCH AS TO CAUSE SAID WORKINGSECTION TO GROW AT A RATE COMMENSURATE WITH THE RATE OF WEAR OF SAID DIEON ITS COMPRESSION SIDE, TO MAINTAIN A DESIRABLE CONSISTENCY OF MATERIALEXTRUDED THROUGH SAID DIE AND THEREBY EXTEND THE NORMAL USEFUL LIFE OFSAID DIE.